In the art of making lenses, when a lens, such as a spectacle lens, is processed so that the lens may be fitted into a lens frame of a spectacle frame, the peripheral face of an uncut lens is ground by a grinder, or cut by a cutter. In this manner, the peripheral portion of the uncut lens is form ed into a prescribed shape in accordance with data corresponding to the shape of the lens frame of the spectacle frame.
Prior art examples of the known processing apparatus for this purpose include, as disclosed in Japanese Patent Application Laid-Open No. 2002-18686, apparatuses in which a rotating tool (a grinder), which can be freely rotated to grind the peripheral face of the lens, is disposed around a shaft on a base. The position of lens grinding or cutting is set by driving a shaft supporting the lens, which can be freely swung relative to the shaft of the rotating tool, towards the shaft of the rotating tool by an arm, and rotating the lens around the axis thereof.
In these apparatuses, the depth of processing of the lens is decided in accordance with the swing angle of the arm, and the position of grinding is obtained in accordance with the rotation angle of the shaft of the lens. The peripheral portion of the lens is processed in this manner in accordance with data corresponding to the shape of the lens frame.
However, in the above prior art apparatuses, the lens processing depth of the lens is correlated to, and must be converted into, the swing angle of the arm. The calculation for converting the depth of lens processing of the lens into the swing angle of the arm is conducted by the control portion of the processing apparatus at portions along the entire periphery of the lens. This calculation has drawbacks in that, since many calculations of the floating point are required, and the data describing the shape of the lens frame is three dimensional data, the calculation load on the CPU (the microprocessor) of the control portion is very great, and the amount of time required before the calculation is completed at portions along the entire periphery of the lens (or the amount of data necessary for starting the processing) is very long. Therefore, a great time lag arises between the initial time directing the apparatus to start the processing of the lens (i.e., the time when the starting switch is pushed) and the time lens processing actually starts. Consequently, the entire time to complete the lens processing, including this time lag, increases. One solution for decreasing this time lag is to use a CPU having a greater calculation ability. However, the drawback of this solution is that the cost of installation of these type of calculation devices, such as a high performance CPU, markedly increases, which translates to increases in the cost of production of these apparatuses.
In the above conventional apparatuses, the lens is pressed to the rotating tool by the swing of the arm and the processing is conducted. However, the above apparatuses have drawbacks because the processing pressure (which is defined as the pressure of contact between the lens and the rotating tool) changes in a small amount depending on the swing angle. Therefore, it is necessary to finely control the arm at every swing angle in order to obtain a uniform processing pressure at every portion along the entire periphery of the lens while the arm applies force. Such fine control of the arm further increases the calculation load on the control portion because the required processing pressure varies depending on the material of the lens and the thickness of the peripheral portion of the lens.
Moreover, the above apparatuses have a further drawback in that various component mechanisms are arranged on a horizontal plane, which increases the size of the apparatus, and the area required for installation of the apparatus increases.
The present invention has been made to overcome the above problems and has an object of minimizing the production cost while minimizing the time required for converting the data describing the shape of the lens frame into the data necessary for the lens processing. Another object of the present invention is to improve the accuracy of lens processing by maintaining the processing pressure on the lens uniformly along the periphery of the lens.